Process for producing elongated, freeflowing metal particles



July 4 1967 J, F. JOYCE ETAL 3,329,746

PROCESS FOR PRODUCING ELONGATED, FREE-FLOWING METAL PARTICLES Filed Nov. 12, 1964 ATTORNEY6 United States Patent 3,329,746 PROCESS FOR PRODUCING ELONGATED, FREE- FLOWING METAL PARTICLES John Frederick Joyce, Mechanicsville, John Harry Jackson, Richmond, and Robert Orin Brewer, Chesterfield County, Va., assignors to Reynolds Metals Company, Richmond, Va., a corporation of Delaware Filed Nov. 12, 1964, Ser. No. 410,363 8 Claims. (Cl. 264--8) The present invention relates to novel methods for centrifugally casting metal particles. More particularly, the invention is concerned with the production of centrifugally cast particles of free-flowing elongated shape, especially particles of aluminous metals (containing at least 50% aluminum by weight) which are to be rolled into strip by the Daugherty method (US. Patent 3,076- 706).

Molten metals can be subdivided into various shapes by centrifugal action. Hair-like filaments of lead can be made, for example, by casting through very fine openings in a revolving pot (e.g., as taught in US. Patent 2,211,- 775), or spherical pellets of steel can be made, for example, by means of a spinning disk closely surrounded by a cylindrical wall of Water created by centrifugal action (e.g., as taught in US. Patent 2,439,772). The type of elongated aluminous particle preferred for the purpose of the above-mentioned Daugherty rolling method, however, have heretofore been centrifugally cast through openings in a revolving pot, and it had been considered necessary for these particles to travel a considerable distance in free flight through a cooling atmosphere, such as air, in order to give them time to solidify substantially before striking a solid or liquid collecting surface. This has required a relatively large and expensive installation, since the particles must not only fly a considerable distance but also be expelled in all directions by the spinning pot.

It has now been discovered that metal particles of the desired free-flowing elongated shape can be formed by casting centrifugally through the openings of a revolving pot, with only a very short distance of throw into a body of coolant liquid, where the particles are cooled from substantially molten to wholly solid condition. It has also been discovered that in the desired shape of the particles, it is necessary to heat the liquid substantially above room temperature toward its boiling point. Apparently, the liquid must reach its boiling point almost instantaneously each time a particle strikes it, forming a cushion of gas boiled off the liquid adjacent the particle. While the invention is primarily useful in connection with aluminous metals east through air into water, it is also applicable to other metals generally (e.g., copper, zinc, lead, nickel, iron, beryllium and beryllium aluminum alloys), to other ambient atmospheres, such as nitrogen or carbon dioxide, and to other coolant liquids (e.g., ethyl alcohol).

For a better understanding of the invention, and for other details and advantages of the invention, attention is now drawn to the accompanying drawing, in which there is shown, for purposes of illustration only, a present preferred embodiment of the apparatus for practicing the invention. I In the drawing:

FIGURE 1 shows a vertical section through the axis of apparatus for centrifugal casting of metal particles;

FIGURE 2 shows a plan view of the apparatus shown in FIGURE 1;

FIGURE 3 shows an enlarged view of a portion of a horizontal section through the rotating pot in the apparatus shown in FIGURE 1; and

FIGURE 4 shows some typical metal particles produced in the apparatus of FIGURE 1.

Referring now more particularly to the drawing, the illustrated apparatus comprises a tank 10 having a vertical cylindrical wall 12, an open upper end, and a bottom end closed by a wall 14. The side wall 12 is secured to fixed supports 16 to hold the tank stationary. A vertical drive shaft 18 concentric with wall 12 extends through a sealed opening in wall 14 and is journaled in a pair of thrust bearings 20 mounted in fixed supports 22 below wall 14. A drive pulley 26 is keyed to the lower end of shaft 18, and a solid disk 28 is screwed tightly onto the threaded upper end of shaft 18. A cylindrical pot 30 is fixed to the top of disk 28. Shaft 18, pulley 26, disk 28 and pot 30 are concentric and rotatable as a unit on bearings 20 when pulley 26 is driven by a belt from a motor (not shown).

The top of pot 30 is open, and a plurality of passages 32 extend through the cylindrical side wall 34 of pot 30. The passages 32 can extend radially, but preferably slant back as illustrated in FIGURE 3 (where the arrow 35 indicates the direction of rotation of the pot).

In operation of the illustrated apparatus, a suitable coolant liquid 36, such as water, is poured into tank 10 until a liquid level is reached which would submerge at least a substantial part of the pot 30 if the shaft 18 were not being rotated. If it is desired not to allow the liquid to wet the pot, the shaft 18 can be driven as the liquid is fed into the tank 10. When it is desired to operate the apparatus, the shaft 18 is driven at sufficient speed to cause the outer periphery of disk 28 to rotate the adjacent portions of the liquid in the tank until a vortex of liquid is created and, as a result, the liquid 36 is forced upwardly along the tank side wall 12 until an annular wall 38 of liquid surrounds the pot 30. The inside surface of liquid wall 38 extends almost vertically upwardly from the outer periphery of disk 28, and is therefore spaced almost a uniform distance from the side wall 34 of pot 30 by a distance only slightly greater than the radius of disk 28 less the radius of pot 30. Since the disk 28 and pot 30 rotate at the same speed, the inner surface of liquid wall 38 tends to approach the same rotational speed as pot 30. Friction of the liquid wall 38 against the stationary side wall 12 of tank 10 has some retarding effect, but this is not observed to be great, especially at the surface of the liquid surrounding pot 30.

When the vortex has been created as described above, and preferably when the pot 30 has been suitably preheated to about the temperature of the molten metal to be poured into it, a stream of molten metal 40 is poured progressively into the upper end of pot 30, and the molten metal is impelled through and out of the pot openings 32 by the centrifugal action of the rotating pot. The size of the pot and the speed of rotation are such that the molten metal leaving the openings 32 forms elongated particles 44 travelling almost horizontally to the inner surface of the liquid wall 38.

It is important that the temperature of the liquid Wall 38, particularly adjacent its inner surface around pot 30, should be maintained at an elevated temperature approaching its boiling point, so that the substantially molten particles 44 will boil the liquid upon contact with it and thereby develop a cushioning gas around the particle in the liquid, as this evidently prevents splattering the molten particles against the wall of liquid. Whatever the explanation may be, tests show that the particles become misshapen when they strike the liquid at substantially room temperature, whereas particles of the desired elongated and free-flowing shape are obtained when the coolant liquid into which they are cast has a suitably elevated temperature. This temperature should be in the range between the boiling temperature of the liquid and about 100 F. below the boiling point, and preferably should be 'between 5 F. and 60 F., inclusive, below the boiling temperature of the liquid. The liquid must, of course, have a boiling point below the freezing point of the metal to be cast. The liquid can be preheated before it is fed to the tank 10, and the molten metal adds more heat, so that progressive substitution of cooler liquid is necessary to control the liquid temperature during a long run. For convenience of preheating the liquid, burners 42 are mounted below the bottom wall 14 of tank 10.

The following tests were run using a tank 18 inches in diameter and 20 inches deep, except in the case of test 9, when a tank of 4 foot diameter and about the same height was used instead. The pots all had an outer diameter of 2% inches and a height of 8 inches. In the case of all the tests except 6 and 7 the passages through the side of the pot were angled as shown in FIGURE 3. In the case of test 7 there was less angle, and in the case of test 6 the passages extended radially from the center of the pot. The disk was mounted directly below the pot and had a diameter of 8 inches and a height of 2 inches. The bottom of the disk was spaced 2 inches above the bottom of the tank. In each case Water was used as the coolant liquid, and the vortex extended from the outer periphery of the disk to almost the top of the tank. The water was preheated to measured temperatures before the cast was made, and in no case was the temperature increased by the heat of the particles more than about 7 F. above the initial water temperature. The results of the tests are summarized in the following table:

ALUMINUM ALLOYS 4i metal, other apparatus based on the same basic principles can operate continuously by continuously feeding coolant liquid of controlled temperature into the tank while continuously withdrawing liquid from the tank together with the metal particles in the latter liquid. Among other possible variations are rotating the pot and disk independently of each other for best performance of each, locating the pot suliiciently above the disk to keep the pot out of the coolant liquid when the disk is not rotating, and running 10 the pot faster or slower to get finer or coarser particles.

While present preferred embodiments of the invention, and methods of practicing the same have been illustrated and described, it will be understood that the invention is not limited thereto but rather by the following claims.

1 We claim:

through its sides, said liquid having a boiling point below the freezing temperature of said metal and the general temperature of the portion of said wall of liquid nearest said pot being in the range between the liquid boiling point and about 100 'F. below 5 said boiling point;

rotating said pot about its axis;

feeding molten metal into said pot;

expelling said metal from said openings so as to form molten elongated particles in the space between said pot and said liquid;

passing said particles into a heat exchange relationship with said liquid;

vaporizing the liquid adjacent said particles, thereby withdrawing heat from said particles and minimizing distortion of said particles caused by impact with the surface of said liquid; and

passing said particles into said liquid so as to further cool them.

2. The process of claim 1 wherein said metal is aluminous metal.

3. The process of claim 1 wherein said liquid is water.

4. The process of claim 1 wherein said Wall of liquid is maintained by rotating said liquid in a vortex.

5. The process of claim 1 wherein said vaporizing minimizes said distortion by forming gaseous cushions between said particles and said liquid.

Particles Produced (In Rpm. of Pot terms of free flow- Metal Metal Temp., Water Temp., Pot and Openings ability and elongated F. F. (Initial) Disk Diameter shape suitable for (Inches) rolling (1)-..- 3004 1, 400 1, 300 076 Poor. (2)--.- 3004... 1, 400 1, 300 076 Good. (3).--. 3004.-. 1, 400 180 1, 300 076 Do. (4)---- 3004 1, 400 200 875 125 Very Good. (5)---- 3004 1, 400 212 1, 300 076 Good. (6).--. 13% Si and 1% Fe 1, 300 1, 300 076 D0. (7)-..- o 1, 300 175 1, 300 1875 D0. (8).-.- 1% Ni and 1% Boron 2, 500 1,300 076 Very Good: (9)---- 25% Si 1,800 170 1, 300 076 D0.

OTHER ALLOYS 076 Bad (Splatter).

Good.

I 076 Do. 125 Fair.

1 Hooked tails, irregular shapes. 2 Not as regular in shape.

The particles vary in size depending upon the composi- 6. The process of claim 1 wherein said particles pass tion of the metal, and, to a greater degree, upon pot speed 7 end-first into heat exchange relationship with said liquid.

and hole opening (the latter preferably being in the range of about .04 to .19 inch diameter inclusive). Specimens of particles 44 produced in test 4 above are illustrated in FIGURE 4. While the specific apparatus of the tests is suitable for testing batches of a few pounds of 75 7. A process for producing solid, free-flowing elongated aluminous metal particles comprising the steps of:

disposing within a tank a hollow pot having openings of diameters of from about 0.04 inch to about 0.19 inch extending through it sides, and a body of water;

rotating said water in a vortex so as to maintain a Wall of water spaced from and extending around said pot, the general temperature of the portion of said Wall of water nearest said pot being from about 152 F. to about 207 F.;

rotating said pot about its axis;

feeding molten aluminous metal into said pot;

expelling said aluminous metal from said openings so as to form molten elongated particles in the space between said pot and said Wall of water;

passing said particles end-first into a heat exchange relationship with said Water;

vaporizing the water adjacent said particles, thereby Withdrawing heat from said particles and forming between said particles and said Water cushions of steam which minimize distortion of said particles caused by impact with the surface of said water; and

passing said particles into said water so as to further cool them.

8. The process of claim 7 wherein said water is roated and said vortex maintained by rotating about the axis of said pot and said vortex a disk disposed at the surface of said vortex.

15 ROBERT F. WHITE, Primary Examiner.

WILLIAM J. STEPHENSON, Examiner.

J. R. HALL, Assistant Examiner. 

1. A PROCESS FOR PRODUCING ELONGATED, FREE-FLOWING METAL PARTICLES COMPRISING THE STEPS OF: PROVIDING A WALL OF LIQUID SPACED FROM AND EXTENDING AROUND A HOLLOW POT HAVING OPENINGS EXTENDING THROUGH ITS SIDES, SAID LIQUID HAVING A BOILING POINT BELOW THE FREEZING TEMPERATURE OF SAID METAL AND THE GENERAL TEMPERATURE OF THE PORTION OF SAID WALL OF LIQUID NEAREST SAID POT BEING IN THE RANGE BETWEEN THE LIQUID BOILING POINT AND ABOUT 100*F. BELOW SAID BOILING POINT; ROTATING SAID POT ABOUT ITS AXIS; FEEDING MOLTEN METAL INTO SAID POT; EXPELLING SAID METAL FROM SAID OPENINGS SO AS TO FORM MOLTEN ELONGATED PARTICLES IN THE SAPCE BETWEEN SAID POT AND SAID LIQUID; PASSING SAID PARTICLES INTO A HEAT EXCHANGE RELATIONSHIP WITH SAID LIQUID; VAPORIZING THE LIQUID ADJACENT SAID PARTICLES, THEREBY WITHDRAWING HEAT FROM SAID PARTICLES AND MINIMIZING DISTORTION OF SAID PARTICLES CAUSED BY IMPACT WITH THE SURFACE OF SAID LIQUID; AND PASSING SAID PARTICLES INTO SAID LIQUID SO AS TO FURTHER COOL THEM. 